Compliant acoustic radiating means



Jan. 23, 1962 w. T. HARRIS COMPLIANT ACOUSTIC RADIATING MEANS Filed May 4, 1954 FIG. I.

FIG. 2.

INVENTOR [5019 7 19/4/5975 ATTO R N EY5 United States Patent 3,018,465 COMPLIANT ACOUSTIC RADIATING MEANS Wilbur T. Harris, Southbury, Conn., assignor to The Harris Transducer Corporation, Southbury, Conn., a corporation of Connecticut Filed May 4. 1954, Ser. No. 427,630 25 Claims. (Cl. 340-8) My invention relates to improved electroacoustic transducer means and, in particular, to electromagnetic transducers as of the character described in greater detail in my copendi-ng applications, Serial No. 241,470, filed August 11, 1951 now Patent No. 2,978, 671, and Serial No. 402,426, filed January 6, 1954 now Patent No. 2,903,673.

It is an object of the invention to provide an improved transducer of the character indicated.

It is another object to provide improved means for coupling a transducer of the character indicated to the medium into which the transducer is to radiate or is otherwise to respond.

It is a further object to provide improved diaphragm means for transducers of the character indicated, whereby the effective radiating area of driving parts of the transducer is substantially enlarged.

It is a specific object to provide parasitically radiating means as a functional part of a transducer of the character indicated.

Other objects and various further features of novelty and invention will be pointed out or will occur to those skilled in the art from a reading of the following specification in conjunction with the accompanying drawings. In said drawings, which show, for illustrative purposes only, preferred forms of the invention:

FIG. 1 is a fragmentary sectional view of a transducer incorporating features of the invention;

FIG. 2 is a plan view of the transducer of FIG. 1, on a reduced scale. and partly broken-away; a

FIG. 3 is a fragmentary perspective view of a parasitic diaphragm employed in the transducer of FIGS. 1 and 2; and

FIG. 4 is a view similar to FIG. 1 and illustrating a modification.

Briefly stated, my invention contemplates employment of novel diaphragm means in conjunction with the movable element of an electroacoustic transducer for providing improved impedance-matching characteristics, so that more efficient energy transfer may be possible between the moving transducer element and the radiating medium. Specifically, for the type of compliant diaphragm disclosed in my said application Serial No. 402,426 now Patent No. 2,903,673, I have discovered that the construction lends itself to provision of a parasitically resonant structure which may be continuous with or adjacent to the electromagnetically driven area. Thus, one continuous large-area diaphragm may comprise a radiating.

surfarx, with a backing surface connected thereto by uniformly compliant structure, so as to permit oscillation between said surfaces when a part of the backing area is driven. The driven part of the diaphragm area may be excited a wavelength or a substantial fraction of a wavelength laterally away from the outer limit of the diaphragm means, and still the entire diaphragm means will resonate, the outer part parasitically and in an appropriate phase relation with the driven part.

In theforms to be described, I find it convenient to employ separate driving and parasitic diaphragms. In one case, the parasitic-diaphragm structure, complete with sealing and sound-decoupling (or reflecting) backing, may be removably secured to an otherwise fully assembled transducer. In the other form, the parasitic diaphragm 2 is assembled and sealed as an integral part of the entire modating the same may be filled with plastic material,

but, for simpilicity, I have simply shaded the entire coil openings as being occupied by winding 16.

As more fully explained in the said copending patent applications, the electrodynamic strips supported in the respective flux gaps are the driving vibratile elements of the transducer. Thus, a coil may comprise a first leg or stretch 17 in the gap 11 and a second leg or stretch 18 in the gap 12. The coil 17-18 may be the first of a plurality of similar structures extending to the left of that shown in FIG. 1; but, in FIG. 2, I indicate that the transducer may comprise merely the single coil 17-18. This coil 17-18 may be developed helically from strip ma-' terial, such as soft bus-bar stock, laminated and consolidated into a single rugged vibratile element.- Coil 17-18 may be yieldably supported by pads 19 of acoustically low-impedance material, such as air-filled rubber.-

The diaphragn means for coupling the energy available in the moving coil 17-18 to the medium into which the energy is to be radiated may comprise essentially a radiating surface 20 and a driving or backing surface 21, said surfaces being connected to each other through a suitable compliance. The coil. 17-18 may be directly supported on the back surface 21, but, in the form shown, I facilitate assembly by mounting the coil 17-18 on a suitably shaped raised part'or pedestal 22, which may be of insulating material and formed as a part of or secured to a mounting plate 23. The plate 23 may be secured, as by bonding, to the backing surface 21.

Th compliance connecting the two surfaces or diaphragms 20-21 may be a matrix of springs or may be defined by Staggered slotted laminations rrmning parallel to the radiating surface 20. However, in the form shown, I indicate my preference for a unitary diaphragm construction in which the surfaces 20-21 and the compliant connection are all integrally formed. In this construction, the diaphragm means comprises a consolidated stack of transverse laminations, one of which is shown in full in FIG. 1. The compliance is derived from local weakening occasioned by a staggered orientation of slots 24 in one row, with respect to slots 25 in another row, and, if desired, with respect to slots 26 in a-third row, depending upon the compliance needed for particular applications. The consolidated stack may be rigidly bonded together and secured, as by longitudinally extending tie rods or bolts 27, and the compliant means will be understood to provide a plurality of spaced compliant connections between surfaces 20-21 distributed over the efiective areas of these'surfaces.

In accordance with the invention, the diaphragm means, which may be of the composite construction described at 20-21, may be of substantially more extensive effective area than that subtended by the driving elements 17-18, and yet the entire diaphragm means may appear to the medium as a radiator, thus providing improved impedance-matching or coupling to the medium and avoiding losses due to spill-over near the lateral limits of the driv-.

ing elements. a

In the form shown in FIG. 1, I have divided the diaphragm means into discrete parts, thereby providing physical separation between the driven diaphragm 2021 and what may be termed a parasitic diaphragm or baflie 29. In order that the parasitic diaphragm 29 shall resonate with substantially the same characteristics as the driving diaphragm, the parasitic construction may be generally similar. Thus, diaphragm 29 may comprise a radiating surface or member 30 and a backing surface or member 31, connected by compliant means comprising staggered rows of slots 32. The laminated nature of the parasitic diaphragm construction will be apparent from FIG. 3. Tie bolts 33 may extend the full length to hold the consolidated stack permanently assembled and, if desired, to secure the ,same to the end flange 34 of a mounting-plate 35. The base plate 35 is preferably spaced from the backing surface or member 31, and this space includes an air pocket 36, thereby substantially duplicating the conditions existing on the non-radiating side of the driving diaphragm 20. The batfle structure 29 may be a complete subassembly removably secured as by bolt means 37 to a part 38 of the frame or housing 39 for the transducer assembly. The air pocket 36 may be defined by a bag of acoustically transparent material, such as-rubber, neoprene or thelike, forming part of a boot 40 encasing the laminated structure. Both the driving diaphragm and the parasitic diaphragm may he of laminated metal or plastic,'depending upon the compliance characteristics required.

To complete the transducer, the magnetic-core means may be secured against side plates of the transducer I housing 39 and spaced from back plates 41 so as to define with the back of the core means 10 a pressureequalizing cavity 42 for rendering the response of the transducer less depth-dependent. For pressure-equalin'ng purposes, a cavity 42 may contain an inflatable bag 43, as of neoprene or the like, and the space between the bag 43 and the back plate 41 may be freely flooded by means of a bleed opening 44. I have suggested by dashed outlines 45 that fluid-communication passages may be located at the ends of the elongated gaps 11-12 to provide free pressure communication between these gaps and the space 42 over the pressure-equalizing bag 43. To render the transducer impervious to moisture, the entire device may be heavily coated with rubber, neoprene or the like, and locally flexible reinforcement means 46 may protect the outer rubber casing or boot 47 at the overlap between fixed and moving parts -39. At least for the area over diaphragm 20, boot 43 will be understood to be of sound-transmitting character.

In operation, the diaphragm 20 will function as described in my said copending application Serial Number 402,426, now Patent No. 2,903,673. At the same 50 time, the parasitic diaphragm or baflle 29, possessing, as it does, a moderate or high mechanical Q, will abstract from the medium excited by diaphragm 20 energy at or near the resonant frequency; and, because the resonant characteristics of the two diaphragms 20-29 are pref- 65 erably substantially the same, the parasitic diaphragm 29 will reradiate as it resonates sympathetically and substantially in phase with the diaphragm 20. The presence of the diaphragm or baflle'29 thus serves to increase the exhibit characteristics which are in substantially all 66 respects similar to those described for the case of FIGS. 1 to 3. The principal difference between the two structures is that in FIG. 4 the parasitic diaphragm 50 and the radiating or driven diaphragm 51 are mounted in close point of thrust application. resonant characteristics in the parasitic diaphragm 50, I

show a similar slotting at 55 at the point of compliant connection to a backing plate or counterweight member 56. Member 56 may constitute the mass equivalent to coil means 17, and it reacts with the radiating face of parasitic diaphragm 50, through the compliant connection.

Other parts of the structure of FIG. 4 may resemble those described for FIG. 1, and at I suggest that the construction of FIG. 4 lends itself to pressure-compensating or depth-compensating treatment. It will .be noted that the passage 45 is, in reality, freely communicable with the air space on the backside of parasitic diaphragm 50, so that both the radiating and the parasitic diaphragm are uniformly corrected for depth-dependence. In order to mechanically locate coils 17 against damage, I :show cushions 57 of yieldable material located. laterally between points of thrust application to the respective diaphragm parts.

In the description thus far, and whatever the embodiment of the invention, I have generally referred to my composite diaphragrns as including opposite surfaces con.- nected by a compliance; these parts may also be viewed from the aspect such that the compliant connections extend between two particular reacting masses. Thus, in FIG. 1, the radiating members or masses 20-30 are compliantly connected to their corresponding driving or backing members or masses 21-17--18 and 31, respectively. Also, since the radiating members 20-30 and -51 are thick and stifi and laterally extensive, and since they function as pistons essentially in a single plane, -I find it convenient to refer to them as planar radiating slabs. In every case, the planar radiating slab is compliantly connected to a reacting counterweight, which in FIG. 4 is substantially only member 56 or coil 17, and which in FIG. 1 is either the backing member 31 or member 21 (plus coil 1718), as. will be understood. 1

It will be seen that I have described relatively simple means for increasing the effective radiating or response area of'a given transducer construction. The presence of the parasitic diaphragm permits the driven diaphragm 45 to bear substantially all the resistance of the medium and to relieve the driven diaphragm from reactive components of coupling to the medium. The bafile construction may be fully pressure-compensated for operation at varying depths and, in the specific form of FIG, 1, the separate unitary construction of the battle 29 makes possible ready replacement of battles 29 of slightly different resonant characteristics in order to produce given desired results.

resistance which the medium presents to the driven 60 While I have described the invention in detail for the preferred forms illustrated, it will be understood that modifications may be made within the scope of the invention as defined in the claims which follow.

I claim:

1. Incombination, for underwater acoustic radiation, diaphragm means comprising two spaced surfaces and a compliance therebetween, and electromechanical means in driving relation with one of said surfaces at a location laterally remote from one edge of said diaphragm means, whereby said edge and the other surface of said diaphragm means near said edge may be essentially uncoupled to said electromechanical means except through the liquid acoustic medium but may nevertheless resonate parasitically. I

2. In combination, for underwater acoustic radiation, diaphragm means comprising adjacent driven and unside-by-side adjacency without any interposed barrier. driven surfaces, each of said diaphragm means further This construction necessitates assembling the parasitic diaphragm 50 in the same structure as the main body of the transducer, and encasing both diaphragms 50-51 with common seal or boot means 52. In the arrange comprising separate backing surfaces coupled to said firstmentioned surfaces by separate compliances, each of said diaphragm means being resonant at substantially the same frequency, and electromechanical means in driving relament of FIG. 4, the compliant connection between A.C.' w tion with the backing surface for said driven diaphragm.

thereindefining a plurality of laterally spaced uniform compliant connections between said surfaces, whereby said body between said surfaces may be stitfiy compliant, and electrodynamic means coupled to said responsive dia phragm means.

4. In a transducer for underwater acoustic radiation, magnetic-core means defining a plurality of spaced elongated gaps, a movable strip of conducting material including opposed legs in the respective fields of two of said gaps, a first diaphragm including a radiating surface exposed to the radiating medium and coupled to said strip through a stiff-spring compliance, and a second diaphragm adjacent said first diaphragm and comprising a radiating surface exposed to the medium and substantially in the plane of said first-mentioned radiating surface, and a reaction mass behind the radiating surface of said second diaphragm and connected thereto through a stifi-spring compliance.

7 5. A transducer according to claim 4, in which a third diaphragm similar to said second diaphragm is mounted adjacent said first diaphragm at a location laterally opposed to said second diaphragm.

6. In combination, for underwater acoustic radiation, transducer-housing means acoustically open on a radiat- -ing side thereof, magnetic-core means contained within said housing means and defining on said open side a plurality of spaced elongated gaps, a movable strip of conductive material including opposed legs in the respective fields of two of said gaps, a compliant resonant radiating diaphragm driven by said movable strip and covering an area of the open side of said housing and exposed to the radiating medium, and a parasitic compliant resonant diaphragm of resonant properties substantially matching those of said driving diaphragm and exposed to the medium in remaining open area on the open side of said housing.

7. The combination of claim 6, in which a dividing wall of said housing extends between said diaphragms.

8. The combination of claim'7, in which an acoustically transparent boot covers the radiating surface of said driving diaphragm and extends into sealing con-tact with said dividing wall to the exclusion of said parasitic diaphragm, said parasitic diaphragm being removably secured as a unit to said housing independently of said radiating diaphragm.

- 9. The combination of claim 6, in which said diaphragrns are mutually adjacent without any barrier therebetween.

10. The combination of claim 6, in which a single continuous boot of acoustically transparentmaterial covers the radiating surfaces of .both said driving and parasitic di-aphragms.

11. As an article of manufacture, a compliant parasitic diaphragm for directionally responsive liquid-immersed application, comprising substantially coextensive driving and backing surfaces connected to each other by stifily compliant means, acoustically transparent means encasing said diaphragm and defining an air-filled pocket on the backside of said diaphragm and substantially coextensive therewith.

12. As an article of manufacture, a compliant parasitic diaphragm comprising driving and backing surfaces connected to each other by compliant means, acoustically transparent means encasing said diaphragm and defining an air-filled pocket on the backside of said diaphragm and substantially coextensive therewith, said driving surface and said compliance and said backing surface being defined by a consolidated stack of transverse laminations with aligned slotted openings-so as to establish compliant areas between said surfaces.

13. In an underwater transducer of the character indicated, magnetic-core means comprising a plurality of pole pieces oriented to define a plurality of spaced elongated gaps in substantially a single plane generally normal to the principal response axis of said transducer, a moving conductive coil including two opposed legs movably supported in two of said gaps, a diaphragm comprising a driving surface fixedly carryingsaid moving coil and a radiating surface connected to said driving surface through a stiff compliance, a rigid housing fixed-1y supporting said magnetic-core means and defining between said core means and a part of said housing a pressureequalizing cavity with an external opening on a side other than the radiating side of said transducer, a collapsible flexible bag within said cavity and covering said opening, whereby fluid may enter said opening and fill said bag, there being a fluidmmmunicating opening between one of said gaps and the other side of said collapsible bag, whereby air within said transducer may be maintained under ambient fluid-pressure conditions, and a baflle comprising a driving surface alongside the driving surface of said diaphragm and a backing surface of mass substantially equal to that of said driving surface and connected to said driving surface through a stiff compliance substantially matching that of said diaphragm.

14. A transducer according to claim 13, and an airfilled bag of yieldable material immediately behind the backing surface of said bafile.

15. A transducer according to claim 13, in which free fluid-communication with said bag and within said transducer is substantially coextensive with the backing sur faces of both said diaphragm and said bafiie.

16. As an article of manufacture, a compliant parasitic diaphragm comprising driving and backing surfaces connected to each other by compliant means, said surfaces and compliant means being defined by a consolidated stack of transverse laminations with aligned slotted openings, said slotted openings extending inlateral rows, there being a plurality of rows with the slots of adjacent rows in laterally staggered relation, and an acoustically decoupling pocket coextensive with said backing surface;

17. An article according to claim 16, and including mounting means connected to longitudinal ends of said stack at a location intermediate said driving and backing surfaces.

18. An article according to claim 16, in which said mounting means includes atie rod passing through'said stack and projecting out both ends thereof;

19. In combination, two diaphragms supported in sideby-side adjacency, one of said diaphragms comprising a radiating surface and a backing surface connected thereto by a compliance, and electromechanical means coupled to the other of said diaphragms and responsive to a frequency of the order of magnitude of the resonant frequency of said one diaphragm.

20. In combination, a primary electromagnetically driven resonant radiator for underwater radiation, and a juxtaposed secondary resonant radiator structurally separate from and unconnected to said primary radiator, said radiators being resonant at substantially the same frequency and both being exnosed to an external medium, whereby said secondary radiator may radiate through coupling through the medium when said primary radiator is driven at substantially said frequency.

21. In combination, for underwater use, a primary driven radiator including a planar radiating slab, and a juxtaposed secondary resonant radiator resonant at the driven frequency of the primary radiator and including a planar radiating slab adjacent and substantially coplanar with said first-mentioned radiating slab.

22. A secondary underwater radiator, comprising a planar radiating slab coupled to a counterweight by comdependently connected to the back of said slab means at 15 8 spaced locations by compliant means, an air-compliance means behind said counterweights to decouple the same, one of said counterweights including a driving element.

References Cited in the file of this patent UNITED STATES PATENTS 1,563,626 Hecht Dec. 1 1925 1,604,532 Riegger on. 26, 1926 1,988,250 Glson Jan. 15, 1935 2,451,968 Murdoch Oct. 19, 1948 FOREIGN PATENTS 29,978 Sweden Nov. 2, 1909 155,569 Great Britain Feb. 28, 1922 

